A gas insulated switchgear uses an SF6 gas having superior insulation performance as an insulation medium, the use of which, however, is being reduced because of its global warming potential about 24000 times as high as that of carbon dioxide. Nitrogen, carbon dioxide, and dry air are used as an alternative gas. However, these gases are inferior to an SF6 gas in insulation performance.
In a case where metal foreign matter in the order of several mm is present in the gas insulated switchgear, the metal foreign matter is likely to adhere to a surface of an insulation structural member and it is known that insulation performance is deteriorated considerably by adhesion of metal foreign matter. When the alternative gas specified above is used as an insulation gas, a degree of deterioration is worsened. Various methods have been proposed as a countermeasure against metal foreign matter, such as installation of a metal foreign matter trapping device at a bottom of the ground tank. It is, however, difficult to achieve 100% trapping performance. Hence, it is necessary to design the insulation structural member to withstand a lightning waveform voltage and a switching surge voltage as a test voltage even when these voltages are applied while metal foreign matter adheres to the insulation structural member.
In view of the background as above, there is a technique of enhancing insulation performance of an insulation structural member (insulation spacer) in a gas insulated device in the related art. For example, there is disclosed a technique for an electrical device having an insulator for which a voltage may possibly be applied along a surface thereof. According to this technique, a cover portion made of an ablation material that generates a gas when heated is formed on the surface of the insulator (for example, see PTL 1).